The invention generally relates to a harmonic rejection mixer.
A conventional wireless receiver system may include at least one mixer, for purposes of downconverting the frequency of the incoming wireless signal. More specifically, the mixer typically multiplies the incoming wireless signal with a local oscillator signal to produce a signal, which has spectral energy that is distributed at sums and differences of the local oscillator and incoming signals' frequencies. If the local oscillator signal is a pure sinusoid that has its spectral energy concentrated at a fundamental frequency, then ideally, it is relatively easy to filter out unwanted spectral energy so that the spectral energy of the filtered signal is generally located at the desired intermediate frequency. However, for certain mixing applications, the local oscillator signal may be a non-sinusoidal, such as a square wave signal, which contains spectral energy that is located at a fundamental frequency and additional spectral energy that is located at harmonic frequencies. Mixing the incoming signal with such a local oscillator signal typically results in undesired spectral energy being located close enough to the desired spectral energy to make the undesired spectral energy relatively difficult to remove by filtering.
Thus, there exists a continuing need for a mixer that rejects harmonic frequencies that may be introduced by a local oscillator signal that is not a pure sinusoid.